Japanese professor Yoji Kimura believes laughter is a weapon that in healthy doses can end the world's wars. To measure it, the expert on communications has invented a machine to chart out laughter -- and a new unit of "aH" to calculate it.

"We have found that children laugh more freely, releasing 10 aH per second, which is about twice as much as an adult," Kimura, a professor at Kansai University in the western city of Osaka, told reporters on Friday.

"Adults tend to calculate whether it's appropriate to laugh and under those restraints they eventually forget how," he said.

"Laughing is like a restart function on a computer. Laughing freely is very important in the course of human evolution," he said.

Kimura, who believes in "a shift from a century of wars to a century of humour and tolerance," has studied the science of laughter for decades in Osaka, the hub of Japan's stand-up comedy scene.

In his theory, human laughter is produced in four successive emotional stages -- letting loose, then deviating from the norm, followed by freely laughing and then having the laughter overflow.

"I believe there is a circuit in the human brain that creates laughter through these steps to the stage of overflowing," Kimura said confidently. "Understanding this mechanism is the door to resolving one secret of human beings."

To measure laughter, he attaches sensors on the skin of a tested subject's stomach, particularly the diaphragm, and detects muscle movements.

"I have a theory that humour detected in the brain gets directly discharged through the movement of diaphragm," he said.

By checking the movement of the diaphragm and other parts of the body, it will be possible to see if a person is only pretending to laugh while also distinguishing different types of laughter such as derision and cynicism, Kimura said.

Kimura wants to make the measuring device as small as a mobile phone and possibly market it as a health and amusement gadget.

Kimura said he planned to present his findings this summer to the US-based International Society for Humor Studies, adding that he looked forward to looking at differences in laughter internationally.